This boosts blood flow and helps you get an erection from sexual activity. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. Sorry something went wrong with your subscription Please, try again in a couple of minutes Retry. Use the oral syringe provided with your medication to measure and take your dose. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not press on the plunger of the syringe.Products and services Erectile dysfunction: Viagra and other oral medications By Mayo Clinic Staff Medicines that you take by mouth are called oral .  · Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 .  · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase .